Polyester resins capable of forming containers having improved gas barrier properties

ABSTRACT

The present invention provides polyester resins useful for forming containers having improved resistance to gas permeability. The containers are formed from a polyester resin which comprises the reaction product of a diol containing up to about 8 carbon atoms and a diacid component which comprises about 5 to 50 mole percent of a first diacid selected from 1,4-phenylenedioxy diacetic acid, 1,3-phenylenedioxy diacetic acid, 1,2-phenylenedioxy diacetic acid, and mixtures thereof, and about 50 to about 95 mole percent of terephthalic acid. The polyester resin has an inherent viscosity of about 0.5 to 1.5. The containers which are provided by the present invention may be in the form of sheet, film, molded articles, such as bottles, and other such structures.

DESCRIPTION

The present invention relates to polyester resins useful for formingpackages for protecting comestibles. More specifically, it relates topolyester resins for forming films and molded containers which haveimproved gas barrier properties.

Presently there is a strong interest in the packaging industry forprotecting comestibles (such as foodstuffs, medicines, and especiallycarbonated beverages) by enveloping the substances in packages which areformed from various polymers. One polymer in which there is anespecially strong interest is polyethylene terephthalate. Containersformed from this material, which may be biaxially oriented, possess manydesirable characteristics. Molded biaxially oriented containers whichare formed from polyethylene terephthalate and certain copolyesters aredisclosed in U.S. Pat. No. 3,733,309. While molded containers formedfrom polyethylene terephthalate have, as indicated, many desirablecharacteristics, there is a need in the art to provide improvedpolyester containers which will have gas permeabilities which are lowerthan those of containers formed from polyethylene terephthalatehomopolymers. Such improved containers would be much more versatile intheir utilization and allow the containers to be used to packagesubstances for which the polyethylene terephthalate containers may notbe suitable.

Another patent, U.S. Pat. No. 2,470,651, discloses the preparation of apolyester of acyl diether dicarboxylic acid and dihydric alcohols andthe use of such polyester compositions as insulating coatings. Suchpolyesters also have good gas barrier properties when formed into film,for example. However, such polyesters do not have the structuralstrength properties to be formed into bottles, such as by blow moldingoperations. However, copolyester compositions which contain 50 percentterephthalic acid provide polymeric compositions which can be formed,for example by blow molding operations, into containers which have goodstructural strength properties and good gas barrier properties useful inthe packaging industry. Such polyester resins, therefore, would be anadvance in the state of the art.

In accordance with the present invention, it has been found that aparticular polyester resin comprises the reaction product of a diolcontaining up to about 8 carbon atoms with a diacid component comprisingabout 5 to 50 mole percent of a first diacid selected from1,4-phenylenedioxy diacetic acid, 1,3-phenylenedioxy diacetic acid,1,2-phenylenedioxy diacetic acid, and mixtures thereof, and about 50 toabout 95 mole percent of terephthalic acid. The polyester exhibits aninherent viscosity of about 0.5 to 1.5.

These polyester resins can be formed into containers having improvedresistance to gas permeability. As used herein, the term "container" isintended to mean shaped articles formed from the specified polyesterwhich are suitable for use in packaging comestibles. Such shapedarticles include not only sheets and films which are extruded from thepolyester and which may be used as such or as barrier layers, containerliners, as components of laminates or other composites, and the like,but also articles which include blow molded containers, such as bottles.

The polyester of the present invention comprises the reaction product ofa diol component and a diacid component. The diol component comprisesone or more diols containing up to about 8 carbon atoms. Examples ofsuch diols include ethylene glycol; 1,4-butanediol;1,4-cyclohexanedimethanol; propylene glycol; diethylene glycol;2,2,4-trimethyl-1,3-pentanediol; 2,2-dimethyl-1,3-propanediol;2,2-diethyl-1,3-propanediol; 2-methyl-2-propyl-1,3-propanediol;1,3-butanediol; 1,5-pentanediol; 1,6-hexanediol;1,2-cyclohexanedimethanol; 1,3-cyclohexanedimethanol;2,2,4,4-tetramethyl-1,3-cyclobutanediol; o-, m-, and p-xylylene diols;etc. The diol component is preferably selected from ethylene glycol,1,4-butanediol, and 1,4-cyclohexanedimethanol, and is more preferablyselected from ethylene glycol and 1,4-butanediol. Most preferably, thediol component comprises ethylene glycol. Additionally, minor amounts(i.e., less than about 50 mole percent, and, preferably, less than about10 mole percent, based on the total amount of diol present in thepolyester) of other known polyester-forming glycols may also beemployed. Such diols may include, for example,2,4-dimethyl-2-ethylhexane-1,3-diol; 2-ethyl-2-butyl-1,3-propanediol;2-ethyl-2-isobutyl-1,3-propanediol; 2,2,4-trimethyl-1,6-hexanediol;4,4'-sulfonyldiphenol; 4,4'-oxydiphenol; 4,4'-isopropylidenediphenol;2,5-naphthalenediol; and other well known polyester-forming diols.

The polyester resin further comprises a diacid component. The diacidcomponent comprises a first diacid selected from 1,4-phenylenedioxydiacetic acid, 1,3-phenylenedioxy diacetic acid, 1,2-phenylenedioxydiacetic acid, and mixtures thereof. The diacid component also includesterephthalic acid. Other well-known polyester-forming diacids may beemployed in minor amounts. Such diacids may include, for example,isophthalic acid, 1,4-cyclohexanedicarboxylic acid, linear lower alkyldicarboxylic acids, etc. The diacid component may also include acidhalides and esters, particularly the lower alkyl (C₁ -C₄) esters of theacids mentioned.

The first diacid, which is selected from 1,4-phenylenedioxy diaceticacid (Formula I), 1,3-phenylenedioxy diacetic acid (Formula II),1,2-phenylenedioxy diacetic acid (Formula III), and mixtures thereof, ispresent in the polyester in a concentration of about 5 to 50 molepercent, based upon the total amount of diacid present in the polyester.##STR1## In preferred embodiments of the present invention,1,3-phenylenedioxy diacetic acid is employed as the first diacid. Thediacid component further comprises 50 to about 95 mole percent ofterephthalic acid.

When the polyester is to be formed into a sheet or film, the firstdiacid is preferably present in an amount of at least about 15 molepercent and, more preferably, in an amount of at least about 30 molepercent (i.e., about 30 to 50 mole percent). When a molded container,such as a bottle, is desired, the first diacid is preferably present inan amount of about 5 to 20 mole percent and, more preferably, is presentin an amount of about 10 to 20 mole percent.

The polyester which is employed in the present invention exhibits anI.V. of about 0.5 to 1.5. The I.V. is measured at 25° C. in a 60/40 byweight mixture of phenol/tetrachloroethane at a concentration of 0.5g/100 ml. Polymers having an I.V. within the range specified above areof sufficiently high molecular weight to be used in the formation of thecontainers of the present invention.

The polyesters of the present invention are synthesized by methodsgenerally known in the art for producing polyesters. The reactants mayall be reacted in a single operation or, alternatively, sequentialoperation may be employed. Temperatures which are suitable for formingthe polyesters generally range between about 180° C. and about 295° C.,with the preferred range being about 200° to 285° C. The reaction may beconducted under an inert atmosphere, such as nitrogen. Preferably, thelatter stage of the reaction is conducted under a vacuum.

Conventional catalysts are employed in the preparation of the polyester.For example, polymerization can be effected in the presence of catalyticamounts of transition metal compounds, such as antimony acetate,antimony trioxide, titanium alkoxides, and organo tin compounds (forexample, stannous alkoxides). Preferred catalysts are titaniumalkoxides, such as titanium tetraisopropoxide, titanium tetrabutoxides,etc. Usually, the catalysts will be present in an amount of about 10⁻⁵to 10⁻³ moles of catalyst per mole of total acid employed.

Of course, suitable additives, such as dyes, pigments, plasticizers,fillers, antioxidants, stabilizers, etc., may be employed inconventional amounts. Such additives may be added directly to thereaction or may be added to the final polymer.

The polyesters described above may be formed into the containers of thepresent invention by conventional plastic processing techniques. Forexample, sheets, films, and other like structures can be formed bywell-known extrusion techniques.

Film or sheet material made from the compositions of the presentinvention is strong, flexible, and clear. It may be formed into articlessuch as wrappers, bags, and the like.

The polyesters may also be used to form a laminating layer between twoor more permeable layers of film. In like manner, a layer of thepolyester of the present invention (preferably, a composition containingabout 50% of the first diacid), may be coextruded as a pipe or similarstructure between two or more permeable layers. The polyesters may alsobe used for dip coating containers from a polymer solution in order toimprove the barrier properties of a package. In each of theseembodiments, the present invention offers the additional advantage ofnot requiring the use of a tie layer.

Molded containers can be made from the abovedescribed polyester bycompression molding, blow molding, and other such molding techniques,all of which are well known in the art. Preferred molded containers arebiaxially oriented blow-molded containers.

The above-described containers of the present invention are ideallysuited for protecting comestibles, such as foodstuffs (especiallycarbonated soft drinks), medicines, and like substances. The advantagesof these containers are due to low oxygen and carbon dioxidepermeability relative to polyethylene terephthalate. Because of thedecreased gas transmission rates of these polyesters, they perform wellin packaging applications where improved gas barrier properties arerequired. Typically, the containers of the present invention exhibit anoxygen permeability of less than about 8.5 (preferably, less than about7.5) and a carbon dioxide permeability of less than about 50(preferably, less than about 30), measured as cubic centimeterspermeating a 1 mil thick sample, 100 inches square, for a 24 hour periodunder a partial pressure difference of 1 atmosphere at 30° C.

This invention will be further illustrated by the following examples,although it will be understood that these examples are included merelyfor purposes of illustration and are not intended to limit the scope ofthe invention.

EXAMPLE 1

This example illustrates the improved gas barrier properties ofcontainers formed of polyethylene terephthalate which has been modifiedwith 5 mole percent of 1,4-phenylenedioxy diacetic acid.

A reaction vessel was charged with dimethyl terephthalate, ethyleneglycol, 5 mole percent of 1,4-phenylenedioxy diacetic acid, based uponthe total diacid present, and 100 ppm of titanium from titaniumtetraisopropoxide. The reaction mixture was heated and stirred undernitrogen at 200° C. for 60 minutes. The temperature was then increasedto 210° C. for 120 minutes until all of the methanol and water haddistilled out of the reaction mixture. The temperature was then raisedto 275° C., the nitrogen was evacuated from the reaction system, and avacuum was applied. The melt condensation was continued at 275° C. for90 minutes under 0.5 mm Hg pressure. The heating was discontinued, thereaction mixture was brought to atmospheric pressure with nitrogen, andthe polymer was collected.

The oxygen permeability of the polyester was determined in cubiccentimeters permeating a 1 mil thick sample, 10 inches square, for a24-hour period under an oxygen partial pressure difference of oneatmosphere at 30° C. using a MOCON Oxtran 100 instrument. The polyesterwas extruded into amorphous (i.e., unoriented) film using a Brabenderextruder at 240°-260° C. The film actually used to measure permeabilitywas 3-8 mils in thickness, but the permeability was converted to a onemil basis using conventional calculations. In like manner, the carbondioxide permeability of the polyester was determined using a MOCONPermatran C instrument.

The results are given in Table I.

EXAMPLE 2

Example 1 was repeated except that 1,4-phenylenedioxy diacetic acid wasreplaced with 1,3-phenylenedioxy diacetic acid. The oxygen permeabilityand carbon dioxide permeability of the polyester were determined as inExample 1, and the results are given in Table I.

EXAMPLE 3

Example 1 was repeated except that 10 mole percent of 1,4-phenylenedioxydiacetic acid was employed. The oxygen permeability and carbon dioxidepermeability of the polyester were determined as in Example 1, and theresults are given in Table I.

EXAMPLE 4

Example 3 was repeated except that 1,4-phenylenedioxy diacetic acid wasreplaced with 1,3-phenylenedioxy diacetic acid. The oxygen permeabilityand carbon dioxide permeability of the polyester were determined as inExample 1, and the results are given in Table I.

EXAMPLE 5

Example 3 was repeated except that 1,4-phenylenedioxy diacetic acid wasreplaced with 1,2-phenylenedioxy diacetic acid. The oxygen permeabilityof the polyester was determined as in Example 1, and the results aregiven in Table I.

EXAMPLE 6

Example 1 was repeated except that 20 mole percent of 1,4-phenylenedioxydiacetic acid was employed. The oxygen permeability and carbon dioxidepermeability of the polyester were determined as in Example 1, and theresults are given in Table I.

EXAMPLE 7

Example 6 was repeated except that 1,4-phenylenedioxy diacetic acid wasreplaced with 1,3-phenylenedioxy diacetic acid. The oxygen permeabilityand carbon dioxide permeability of the polyester were determined as inExample 1, and the results are given in Table I.

EXAMPLE 8

Example 6 was repeated except that 1,4-phenylenedioxy diacetic acid wasreplaced with 1,2-phenylenedioxy diacetic acid. The oxygen permeabilityof the polyester was determined as in Example 1, and the results aregiven in Table I.

EXAMPLE 9

Example 1 was repeated except that 50 mole percent of 1,4-phenylenedioxydiacetic acid was employed. The oxygen permeability of the polyester wasdetermined as in Example 1, and the results are given in Table I.

EXAMPLE 10

Example 9 was repeated except that 1,4-phenylenedioxy diacetic acid wasreplaced with 1,3-phenylenedioxy diacetic acid. The oxygen permeabilityof the polyester was determined as in Example 1 and the results aregiven in Table I.

EXAMPLE 11

A reaction vessel was charged with 22.42 grams of 1,4-phenylenedioxydiacetic acid, 24.60 grams of ethylene glycol, and 100 ppm of titaniumfrom titanium tetraisopropoxide. The reaction mixture was heated andstirred under nitrogen at 210° C. for 60 minutes. The temperature wasthen increased to 220° C. for 120 minutes until all of the water haddistilled out of the reaction mixture. The temperature was then raisedto 260° C., the nitrogen was evacuated from the reaction system, and avacuum was applied. The melt condensation was continued at 260° C. for75 minutes under 0.5 mm Hg pressure. The heating was discontinued, thereaction mixture was brought to atmospheric pressure with nitrogen, andthe polymer was collected. The polymer had an inherent viscosity of0.88. The oxygen permeability and carbon dioxide permeability of thepolyester were determined as in Example 1. The results are given inTable I.

EXAMPLE 12

Example 11 was repeated except that 1,3-phenylenedioxy diacetic acid wasused in place of 1,4-phenylenedioxy diacetic acid. The resulting polymerhad an I.V. of 0.56. The oxygen permeability and carbon dioxidepermeability of the polyester were measured as in Example 1, and theresults are given in Table I.

COMPARATIVE EXAMPLE 1

A control sample of polyethylene terephthalate was prepared according tothe procedure given in Example 1. The oxygen permeability and carbondioxide permeability of the sample were determined as in Example 1, andthe results are given in Table I.

COMPARATIVE EXAMPLE 2

Example 3 was repeated except that 1,4-phenylenedioxy diacetic acid wasreplaced with 2,2'-[1,4-phenylenebis(oxy)]bisethanol. The oxygenpermeability and carbon dioxide permeability of the polyester weredetermined as in Example 1, and the results are given in Table I.

                  TABLE I                                                         ______________________________________                                        Run        Oxygen Permeability                                                                          CO.sub.2 Permeability                               ______________________________________                                        Ex. 1      8.3            47                                                  Ex. 2      7.5            49                                                  Ex. 3      6.3            39                                                  Ex. 4      5.0            26                                                  Ex. 5      6.2            --                                                  Ex. 6      4.8            22                                                  Ex. 7      3.1            18                                                  Ex. 8      3.2            --                                                  Ex. 9      1.0            --                                                  Ex. 10     0.6            --                                                  Ex. 11     0.6            4.5                                                 Ex. 12     0.1            0.6                                                 Comp. Ex. 1                                                                              10.0           59                                                  Comp. Ex. 2                                                                              11.0           63                                                  ______________________________________                                    

An analysis of the data of Table I indicates the superior propertiesexhibited by the polyesters of the present invention which make themextremely advantageous for use in the formation of containers. It willbe noted that the compositions described in the examples, withoutexception, exhibit oxygen and, for those compositions tested, carbondioxide permeabilities below those exhibited by polyethyleneterephthalate as exemplified by Comparative Example 1. The data of TableI further indicate that, while all the compositions are useful for theformation of improved containers, those compositions employing the metaisomer are preferred due to their improved resistance to gaspermeability.

The uniqueness of the polyesters of the present invention and of theproperties exhibited by containers formed therefrom is indicated by acomparison of the Examples with Comparative Example 2, which employs astructurally similar glycol for the second diacid. However, thepolyester of Comparative Example 2 exhibits poor resistance to gaspermeability, whereas the compositions of the Examples of the presentinvention demonstrate a much improved resistance to gas permeability, ascompared to polyethylene terephthalate.

While the invention has been described in detail with particularreference to preferred embodiments thereof, it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

We claim:
 1. A polyester composition capable of being formed into moldedcontainers having good gas barrier properties comprising the reactionproduct of(A) a diol containing up to about 8 carbon atoms, and (B) adiacid component comprising(i) about 5 to 50 mole percent of at leastone first diacid selected from the group consisting of1,4-phenylenedioxy diacetic acid, 1,3-phenylenedioxy diacetic acid and1,2-phenylenedioxy diacetic acid, and, (ii) about 50 to about 95 molepercent of terephthalic acid,wherein said polyester has an inherentviscosity of about 0.5 to 1.5.
 2. The polyester of claim 1 wherein saiddiol comprises ethylene glycol, 1,4-butanediol,1,4-cyclohexanedimethanol, or a mixture thereof.
 3. The polyester ofclaim 2 wherein said diol is ethylene glycol.
 4. The polyester of claim3 wherein said first diacid is 1,4-phenylenedioxy diacetic acid.
 5. Thepolyester of claim 3 wherein said first diacid is 1,3-phenylenedioxydiacetic acid.
 6. The polyester of claim 3 wherein said first diacid is1,2-phenylenedioxy diacetic acid.
 7. The polyester of claim 1 whereinsaid first diacid is present in a concentration of about 5 to 50 molepercent.
 8. The polyester of claim 7 wherein said first diacid is1,4-phenylenedioxy diacetic acid.
 9. The polyester of claim 7 whereinsaid first diacid is 1,3-phenylenedioxy diacetic acid.
 10. The polyesterof claim 7 wherein said first diacid is 1,2-phenylenedioxy diaceticacid.